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Adsorption and desorption characteristics of rare earth ions on halloysite surfaces

Long Qibang, Yan Huashan, Zhou Xiaowen, Qiu Sen, Qiu Tingsheng

Physicochemical Problems of Mineral Processing

2024

Vol. 60, iss. 1

art. no. 185763

Rare earths (REs) are primarily adsorbed in ionic form on the surface of clay minerals such as halloysite in ionic rare earth ores. As a result, understanding the adsorption and desorption behaviors of RE ions on the surface of the halloysite may contribute to clarifying the mineralization process of ionic rare earth ores and provide a theoretical framework for the optimization of the extraction process. The adsorption and desorption characteristics of light (Nd3+), medium (Eu3+), and heavy (Lu3+) RE ions on the surface of halloysite-10 Å were comprehensively examined in this study. Because REs are more inclined to form an outer layer and inner layer adsorption when halloysite is protonated and deprotonated with the range of pH, respectively, pH has a significant impact on how halloysite adsorbs and desorbs. The experiment findings indicate that RE concentration, duration, and pH all increased the adsorption capacity of light, medium, and heavy REEs, and exhibited some selectivity for heavy REEs. Nd3+, Eu3+ and Lu3+ ions adsorption processes on the surface of Halloysite-10 Å are consistent with the Langmuir isothermal adsorption model and pseudo-second-order kinetic equations. The desorption efficiency of Lu3+ decreases dramatically with increasing pH due to hydrolysis and more inner layer adsorption than that of Nd3+ and Eu3+.

Adsorption of hydrated Fe(OH)2+ on the kaolinite surface : A density functional theory study

Wu Hongqiang, Miao Yuqi, Long Qibang, Yan Huashan, Li Yong, Qiu Sen, Wu Hao, Zhao Guanfei, Qiu Tingsheng

Physicochemical Problems of Mineral Processing

2023

Vol. 59, iss. 6

art. no. 174415

The present study employed density functional theory (DFT) to analyze the adsorption configuration and mechanism of Fe(OH)2+ on the kaolinite (001) surface. The findings demonstrated that Fe(OH)2(H2O)4+ is the main type in which hydrated Fe(OH)2+ can be found in aqueous solution. On the surface of kaolinite, Fe(OH)2(H2O)4+ will be adsorbed. There are two forms of adsorption: outer-sphere and inner-sphere coordination (monodentate/bidentate) adsorption. Fe(OH)2(H2O)4+ has a moderate propensity to adsorb on the alumina octahedral sheet of kaolinite when the outer-sphere coordination adsorption takes place. In cases of inner-sphere coordination adsorption, Fe exhibits a tendency to form monodentate adsorption compounds in conjunction with Ou atoms. Additionally, it prefers to create bidentate adsorption compounds through coordination with both Ot and Ou atoms. The adsorption mechanism analysis results show that the ionic property of Fe atom decreases after outer-sphere coordination adsorption. After inner-sphere coordination adsorption, some electrons of Fe atom are transferred to the surface O atom. The presence of electrons between the Fe and O atoms enhances the formation of bonds, hence enhancing the covalent nature of the Fe-O bond. Theoretical FT-IR (Fourier transform infrared spectroscopy) calculations show that the formation of Fe-O chemical bonds. Because of the lower adsorption energy and more chemical bonds, hydrate Fe(OH)2+ is more likely to be bidentate adsorbed on the kaolinite surface.